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Nanotube esd protective devices and corresponding nonvolatile and volatile nanotube switchesNanotube esd protective devices and corresponding nonvolatile and volatile nanotube switches description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060193093, Nanotube esd protective devices and corresponding nonvolatile and volatile nanotube switches. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATION [0001] This application claims priority under 35 U.S.C. .sctn. 19(e) to the following applications, the contents of which are incorporated herein in their entirety by reference: [0002] U.S. Provisional Patent Application No. 60/624,428, filed on Nov. 2, 2004, entitled Nonvolatile Carbon Nanotube Protective Devices (NV-NT-PDs); and [0003] U.S. Provisional Patent Application No. 60/624,297, filed on Nov. 2, 2004, entitled Enhanced CNT Switching Operation. BACKGROUND [0004] 1. Technical Field [0005] The present application generally relates to ESD protections and, more specifically, to the use of nanotube switching elements in the formation of circuits for enhanced electrostatic discharge (EDS) protection of semiconductor, hybrid semiconductor and nanotube, and nanotube-only circuits. [0006] 2. Discussion of Related Art [0007] Electrical overstress resulting from electrostatic discharge (ESD) is a major problem in every generation of electronic devices, resulting in oxide and junction failures such as series resistor rupture, open circuits and short circuits, for example. Nanotube resistors may be used to replace presently used series resistors such as polysilicon, for example, and improve protective device resistance to ESD-induced failure. [0008] FIG. 1 illustrates a prior art protective device (PD) schematic 10 that includes a series resistor 16 and semiconductor diodes 18. An ESD pulse applied to the input pad 12 is attenuated by resistor 16 and semiconductor diodes 18, reducing the ESD voltage applied to node 17, thereby preventing damage to protected circuits 14 as described in the referenced book H. B. Bakoglu, "Circuits, Interconnections, and Packaging for VLSI," Addison-Wesley Publishing Company, 1990, pages 46-51. For some input or output pads there is no series resistance 16, and only semiconductor diodes 18 are used. Resistor 16 may be fabricated using polysilicon or diffusion layers, for example, or other suitable resistive material, and may be in the range of 10 to 100,000 ohms, for example. Conventional resistors fabricated using polysilicon or diffusion layers, for example, can fail in the presence of an ESD pulse, with the resistor becoming an open circuit, for example, due to a combination of current density and temperature. [0009] Prior art protective device structures 10 such as those illustrated schematically in FIG. 1 have high relative capacitance values, 1.5 pF, for example, as described in Bertin et. al. U.S. Pat. No. 6,141,245. If an output driver drives eight chips in parallel as in a memory address line, for example, then the protective device contribution to the capacitive loading is 12 pF. FIG. 3 illustrates prior art structure 39 illustrated in U.S. Pat. No. 6,141,245 in which a fuse 40 is added in series with prior art protective devices, along with a fuse pad, such that current can be forced between the input pad and the fuse pad. After the component is installed in a system, current is forced through the fuse until it open-circuits disconnecting the protective device from the protected circuits to reduce capacitance loading, as described in U.S. Pat. No. 6,141,245. The component cannot be removed and handled again without a high risk of ESD damage because the fuse blow operation is irreversible. [0010] Carbon nanotubes can tolerate current densities in excess of 100 times the current densities of copper, exhibit high thermal conductivity, and do not fail due to overheating as described in the reference Srivastava and Banerjee, "A Comparative Scaling Analysis of Metallic and Carbon Nanotube Interconnections for Nanometer Scale VLSI Technologies," Proceedings of the 21.sup.st International VLSI Multilevel Interconnect Conference (VMIC), September. 39-October 2, Waikoloa, Hi., pp. 393-398, 2004. These, and other properties of carbon nanotubes are described in Nantero carbon nanotube patents, patent publications, dockets, etc. herein incorporated. SUMMARY [0011] The invention provides nanotube ESD protective devices and corresponding nonvolatile and volatile nanotube switches. [0012] Under one aspect of the invention, an electrostatic discharge (ESD) protection circuit for protecting a protected circuit is coupled to an input pad. The ESD circuit includes a nanotube switch electrically having a control. The switch is coupled to the protected circuit and to a discharge path. The nanotube switch is controllable, in response to electrical stimulation of the control, between a de-activated state and an activated state. The activated state creates a current path so that a signal on the input pad flows to the discharge path to cause the signal at the input pad to remain within a predefined operable range for the protected circuit. [0013] Under another aspect of the invention, the nanotube switch, the input pad, and the protected circuit are on a semiconductor chip. [0014] Under another aspect of the invention, the nanotube switch is on a chip carrier. [0015] Under another aspect of the invention, the deactivated and activated states are non-volatile states. [0016] Under another aspect of the invention, the deactivated and activated states are volatile states. [0017] Under another aspect of the invention, the ESD circuit may be repeatedly programmed between the activated and deactivated states so as to repeatedly activate and deactivate ESD protection of the protected circuit. [0018] Under another aspect of the invention, the nanotube switch provides protection based on the magnitude of the signal on the input pad. [0019] Under another aspect of the invention, an electrostatic discharge (ESD) protection circuit is coupled to an input pad for protecting a protected circuit that is also coupled to the input pad. The ESD protection circuit includes a nanotube switch having at least two terminals and at least one control. A first of the two terminals is electrically coupled to the input pad and protected circuit and a second of the two terminals is coupled to a discharge path. The nanotube switch is controllable, in response to electrical stimulation of the control, between a de-activated state and an activated state. The de-activated state presents a relatively high impedance between the first and second terminals of the nanotube switch so that a signal on the input pad passes to the protected circuit substantially unaltered. The activated state presents a relatively low impedance between the first and second terminals of the nanotube switch so that a signal on the input pad flows to the discharge path coupled to the second terminal. The nanotube switch includes a nanotube element having a plurality of nanotubes. The nanotube is sized to produce the relatively low impedance of the nanotube switch in the activated state. The relatively low impedance is sufficient to cause the signal at the input pad to remain within a predefined operable range for the protected circuit. BRIEF DESCRIPTION OF THE DRAWINGS [0020] In the Drawing, [0021] FIG. 1 shows a schematic representation of a prior art conventional protective device; [0022] FIGS. 2A and 2B illustrate a cross section and plan view of a carbon nanotube resistor that may be used to replace a conventional series resistor; Continue reading about Nanotube esd protective devices and corresponding nonvolatile and volatile nanotube switches... Full patent description for Nanotube esd protective devices and corresponding nonvolatile and volatile nanotube switches Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Nanotube esd protective devices and corresponding nonvolatile and volatile nanotube switches patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. 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